Field of the Invention
The present invention relates to a radiofrequency high-output device.
Background Art
In a radiofrequency high-output device, terminals and a frame are brazed on a base plate, and semiconductor chips and matching circuit substrates are mounted in the frame on the base plate. A frame upper surface is covered with a cap to hermetically enclose the interior of the frame.
A CuW member, a Cu—Mo alloy member, a Cu—Mo—Cu multilayer member or the like is used as the base plate by considering heat dissipation from the semiconductor chips and matching in linear expansion coefficient between the semiconductor chips and the base plate. Schemes to develop semiconductor chips of higher outputs have recently been advanced and Cu—Mo—Cu multilayer members having a high heat dissipation characteristic are therefore used.
The base plate has cuts provided at each of its opposite shorter sides. The radiofrequency high-output device is mounted on an aluminum heat sink plate on a customer's circuit board and is fixed with screws inserted in the cuts in the base plate.
The frame is brazed on the base plate. However, the base plate is warped downward after brazing because the linear expansion coefficients of the two members are different from each other. Also, after the semiconductor chips and the matching circuit substrates are mounted with solder, complicated warps result due to a mismatch in linear expansion coefficient between the these component parts. When the device is mounted on the aluminum heat sink plate on the customer's circuit board with screws while having such warps, the warps are corrected but stresses caused in the semiconductor chips and the matching circuit substrates are increased, resulting in cracks or breakages in the component parts. A measure to improve the flatness of the frame upper surface or the base plate lower surface by plane polishing is taken in order to minimize the warp of the base plate. However, the cost of such working is considerably high.
Making thinner a peripheral portion of a heat sink on which semiconductor chips are mounted or providing a groove in the peripheral portion of the heat sink to reduce stress at the time of mounting the semiconductor chips in a device having the heat sink joined to a base plate has been proposed (see, for example, Japanese Patent Laid-Open 7-221265). However, this technique is not effective in solving the above-mentioned problem with fixing of the base plate with screws.